Apparatus for starting and operating gaseous discharge devices



June 22, 1954 A. E. FEINBERG 2,682,014

APPARATUS FOR STARTING AND OPERATING GASEOUS DISCHARGE DEVICES Filed May19, 1952 2 Sheets-Sheet l June 22, 1954 A FEINBERG 2,682,014

APPARATUS FOR STARTING AND OPERATING GASEOUS DISCHARGE DEVICES Filed May19, 1952 2 Sheets-Sheet 2 Patented June 22, 1954 APPARATUS FOR STARTINGAND OPERAT- ING GASEOUS- DISCHARGE DEVIUES Albert E. Feinberg,

Chicago, Ill., assignor to Advance Transformer 00., Chicago, llll., acorporation of Illinois Application May 19, 1952, Serial No. 288,652

9 Claims. 1

This invention relates generally to apparatus for startin and operatinggaseous discharge de vices such as fluorescent lamps.

Particularly, this invention is directed to apparatus in which burn-outsor excessive heat is prevented in certain of the windings of the apparatus under certain emergency conditions. When a fault occurs in adischarge device such conditions arise, and unless some steps are takento incorporate means into the apparatus to prevent the damage,considerable expense results.

The invention is directed to a type of apparatus known as a ballastwhich is connected with a source of low alternating voltage, such as forexample, a 118 volt A. C. line which ignites gaseous discharge devicesof the so-called instant start variety. Such devices are exemplified incommercially known fluorescent lamps and require very high ignitionvoltages, and when operating, also require voltages substantiallygreater than the line voltage. In Feinberg Patent No. 2,558,293, issuedJune 26, 1951, to the assignee of the instant application and entitledApparatus for Starting and Operating Gaseous Discharge Devices Idescribed and claimed a bal last of this type which has gone intoextensive commercial use.

The ballast of Feinberg Patent No. 2,558,293 comprises a three-windingtransformer having a primary winding P, a first secondary winding S1 anda second secondary winding S2, all of the windings being connectedserially in the order named with the secondary windings arranged involtage bucking relationship one to the other. The wLirhngs are allmounted on a unitary elongate core side by side, with the two secondarywindings on opposite sides of the primary winding. There is a shuntbetween the winding S1 and the primary winding P such that certainbenefits are obtained from this winding during startin and durinoperation.

The loose coupling of the primary winding P and the first secondary S1gives rise to a very high leakage reactance in the first secondarywinding. The gaseous discharge devices are adapted. to be connected oneacross the two secondaries and another across the primary and firstsecondarywinding S1 in one case, and one across the first secondarywinding S1 alone and another across all of the windings in the secondcase. Variations are of course possible, but generally there is onegaseous discharge device connected across windings excluding the secondsecondary S2 and including at least the first secondary S1, and a secondgaseous discharge device across windings which include at least both ofthe secondary windings.

The operation of the ballast is fully set forth in the said patent, butwill be repeated briefly here. Presume a ballast in which one gaseousdischarge device is connected across both the primary P and firstsecondary winding S1 and the second gaseous discharge device isconnected across both secondary windings S1 and S2 together. Such aballast is shown generally in Fig. 5 hereinafter described. When theprimary winding P is energized a voltage will be produced in both theprimary winding P and the first secondary winding S1 which will besufiicient to ignite the first gaseous discharge device. When currentflows through the winding S1, because of its high leakage reactance, avoltage will be produced therein which has a phase such as to produce asubstantial component additive relative to the voltage induced in thesecond secondary winding S2. Thus the second gaseous discharge devicewill now ignite. With both of the gaseous discharge devices operating,there will be a series path for the major portion of the current throughthe devices, and the second secondary winding S2, the first secondarywinding S1 being Icy-passed because its high leakage reactance impedesthe fiow of current therethrough. Because of this, the winding S1 canbe, and in commercial versions has been made of a large number of turnsof very fine wire. Obviously since it carries so little current duringoperation, it permits of this and the ballast is thereby rendered verysmall and compact. Likewise very r high ignition voltages can beachieved with very little copper.

Normally, no difiiculties arise in the operation of such ballasts, andsame are now successfully bein used in large quantities. Gaseousdischarge devices used on A. C. circuits are designed to belei-directional with respect to the flow of current. In the case offluorescent tubes, there are two filaments, one at each end, each ofwhich serves both as cathode and anode, but on alternating cycles. Ifthe emissive' properties of a filament are destroyed for some reason orthe other, either through long use or jarring, or the like, then thatfilament loses its ability to be a cathode. It can only be an anode. Theresult is that the discharge device now functions only a rectifyingtube. Fluorescent tubes do not last long on direct current and theirends become blackened through uni-directional flow of current,bombardment of the anode end, and per haps other causes.

Their efficiency is less, and

their use on direct current is avoided also because the ballastsfunction only to provide D. C. resistance.

In the event the above occurs in an ordinary ballast, there is no greatproblem of removing the discharge device and replacing it, but in thecase of the type of ballast above described another problem arises. Inorder to adjust the line power factor, and as an aid in starting, acondenser is usually placed in series connection with the firstdescribed gaseous discharge device. In the event that one of thefilaments of the first gaseous discharge device becomes inoperative as acathode, there will be no direct current passing through the windings ofthe ballast and no harm outside of the possible eventual loss of thefluorescent tube. If, on the other hand, this occurs in the second tube,the current will be forced through the first secondary winding S Sincethe winding is built for extremely low currents, it will either heat upexcessively or burn out. Thus, the ballast must be removed from theinstallation and replaced with considerable expense and inconvenience.

It is therefore the principal object of the invention to provideapparatus of the character described in which all of the benefits ofinvention of the said Feinberg patent are achieved, but in which thepossibility of burn-outs or excessive temperature occurring in thewindings is eliminated.

Still a further object of the invention is to provide apparatus of thecharacter described in which direct current caused by rectifying actionof a fulty gaseous discharge device is prevented from passing throughthe transformer secondaries.

Another object of the invention is to achieve the above objects withoutin any way adversely aifecting the operation of the apparatus andwithout materially increasing the costs thereof.

Still a further object of the invention is to provide apparatus of thecharacter described in which there are a pair of condensers in theseries circuit evolved after both of the gaseous discharge devices areoperating, one of the condensers being in series with the first gaseousdischarge device and the other being in series with the second secondarywinding.

Other objects of the invention will occur as the description proceeds inwhich I have illustrated two examples of an embodiment of the invention.The basic apparatus is capable of considerable variation and themodification thereof which comprises the invention herein is capable ofbeing applied to all of these variations, whether two gaseous dischargedevices or more are used and whether there are more than the threewindings described herein.

In the drawing, in which like characters represent the same or similarparts throughout the several figures thereof:

Fig. l is an electrical circuit diagram of ap paratus embodying theinvention.

Figs. 2 and 3 are side elevational views showing transformerconstructions capable of being used with my invention.

Fig. 4 is an electrical circuit diagram of apparatus embodying theinvention showing a variation thereof.

Fig. 5 is an electrical circuit diagram similar to that of Fig. 1 butnot embodying the invention hereof, same being a diagram of the circuitof the apparatus of the patent hereinabove referred to.

Fig. 6 is an electrical circuit diagram similar to that of Fig. 1 butembodying a modified form of the invention.

Referring first to Fig. 5, same is an illustration of the basic circuitof apparatus described and claimed in the above referred to Feinbergpatent. The invention comprises a modification thereof whereby theresults and objectives are achieved.

As noted above, the said circuit comprises three windings, the primarywinding P, a first secondary winding S1, and a second secondary windingS2, all connected end to end in the order named. The said windings aremounted upon a laminated iron core of the kind illustrated in Figs. 2and 3 and described hereinafter, but not in the same order as connectedtogether. The conventional symbols representing shunts and the core arenot illustrated in order to keep the diagrams as simple as possible, andto enable their illustration in the form shown, i. e., with the windingsplaced in the circuit one after the other. The junction between theprimary winding P and the first secondary winding S1 is designated II]and the junction between the secondaries is designated I l. The gaseousdischarge devices are symbolically illustrated as fluorescent lamps andare designated L1 and L2, that being the ignition order. The left handterminal of the winding P is connected to one side of the line 12 andthe left hand terminal of the lamp L1 is connected by way of lead [3 tothe same terminal. The right hand terminal of the lamp L1 is connectedby way of the lead M with the juncture H. The right hand terminal of thelamp Ia and the right hand terminal of the second secondary winding S2are connected together by way of the lead I5. The left hand terminal ofthe lamp L2 is connected with the juncture H! by way of the lead I6. Thejuncture I0 is also connected with the second side of the line I2.

The voltage sense of each of the windings relative one to the other isindicated by the arrows l1, l8 and [9. The manner in which suchrelationship is achieved is well-known in the art, it being a practicalmatter that all of the windings are wound in the same manner, but theconnections relative to orientation on the core adjusted to achieve theadditive or bucking relationships of their instantaneous voltages.

In operation, as explained, when voltage is applied by the line IE tothe primary winding P, there is a voltage induced in 51 which will'beseen to be additive. The resultant of voltages of primary winding P andfirst secondary winding S1 appears across the lamp L1 and is sufficientto ignite the said lamp. After ignition, current fiows through leads l3and I4 and through the first secondary winding S1. Since that winding isvery loosely coupled relative to the primary, there is a high leakagereactance produced, and the voltage that occurs as a result of the flowof current includes a component that is additive to the voltage inducedby the primary winding P in the winding S2.

Until this occurs, there is not sufiicient voltage across the secondlamp L2 to ignite the same, since the open circuit voltages of therespective windings S1 and S2 are in opposition, and their resultant farless than the ignition voltage of the said lamp L2. Now, however, with avoltage component additive to the induced voltage occurring across thewinding S2, there is sufiicient voltage across the lamp L2 to ignite thesame. When this occurs, the high reactance of the winding S1 opposesflow of current therethrough. Thus ourrent will flow during operationsubstantially through the lamps and the second secondary winding S2, byway of the leads l3, M, and I5. Most of the current of operation willby-pass the winding S1 with a result that the said winding can be madeof extremely fine wire and with a great many turns. In order to aid thestarting at least to some extent and to provide some provision foradjustment of the power factor of the operating circuit, a seriescondenser C is inserted in the lead Hi.

Just to illustrate the nature of the circuit, in the above referred topatent I described an example which was intended for use with what arecommercially known as T-l2 fluorescent lamps, same being 48 inches inlength, 1 inches in diameter, and having a rating of forty watts each.The windings are formed with the primary winding P having 540 turns ofNo. wire, the second secondary S2 having 1270 turns of No. 27 wire, butwith the first secondary winding S1 having 2360 turns of No. wire whichis very fine. Under the operating conditions, the first secondarywinding was found to carry a current of about .030 ampere, which ofcourse is very little. Under these circumstances, the current throughthe lamps, that is, in the series portion of the circuit, is about .435ampere.

Presume that in a construction of this kind something occurs whichadversely affects the operation of the lamp L2 such that one of itscathodes ceases functioning as such. The gaseous discharge is now onlyuni-directional and the lamp is operating as a rectifier. As arectifier, the only current which flows through the lamp L2 and throughthe second secondary winding is direct current. It will be blocked outof the lamp L1 by the condenser C; it will not be afiected by the highleakage reactance of the first secondary winding S1; and consequently itwill pass through the said winding. This current in the winding S1 underthese circumstances may reach almost .300 ampere, or about ten times thecurrent for which the winding is designed.

Under the adverse conditions described above, the winding S1 is certainto overheat and promote dangerous conditions to exist in the vicinitythereof. For example, if occurring in a fixture, it may well become afire hazard, and do other damage. If the wire cannot carry the addedcurrent, which is most likely, the winding will burn out and destroy theballast. Since these ballasts are assembled in metal containers, withvarnished windings in pitch, and usually installed in fixtures, it canbe appreciated that in addition to the cost of a new ballast, there isthe expense of replacement and the inconvenience of loss of function.

My invention results in the alleviation and prevention of the abovedescribed diihculty. The manner in which this is done without materiallyincreasing the cost of the ballast or destroying the efiiciency ofoperation thereof is basically to utilize two condensers to perform thefunction of the condenser C, but to place them in a manher which isadvantageous and which will prevent burn-outs or heating of the windingS1, thereby adding an additional function. The arrangement of thecondensers of the invention further produces a ballast in which when alamp commences to act as a rectifier, it will cease functioning suchthat an observer may immediately now what has occurred. It is to beremembered that in the case of the circuit of Fig. 5, the rec" ifyinglamp will continue to burn (if the winding S1 does not burn out) suchthat the user may not immediately realize that there has been a mishapto the lamp.

Practically speaking, I have substituted for the condenser C a pair ofcondensers each having twice the capacity of C but half the rating (forany given set of conditions), one being placed in the lead [4 as C waspositioned, and the other being placed in series with the secondsecondary winding S2, preferably between the juncture ii and the lefthand terminal of the said winding S2.

In Figs. 1 and 4 I have in which the invention is applied to twovariations of the circuit for preventing the flow of excess currentthrough the winding S1. Each of the circuits of the said Figs. 1 and 4is capable of being utilized in connection with a transformer of theconstruction of either of Figs. 2 or 3. In both transformers, designatedrespectively 26 and 26, there is a rectangular, elongate, shelllike core21 of laminated electrical steel structure having a central elongatewinding leg 22 matingly seated in the shell-like core 2i. The windingsillustrated the manner are all pro-mounted upon the central winding leg22 and the whole assembly pressed home into the core. Note that thewinding P is disposed in the center of the transformer and the secondary windings S1 and S2 are on opposite sides. In each case there is amagnetic shunt 23 which separates the primary winding P from the firstsecondary winding S1 in order that the high leakage reactance which hasbeen described be engendered. It is pointed out that the winding 5: isalso loosely coupled with the primary winding P, but of course to asubstantial degree less than the first secondary winding S1. In the caseof the transformer 20 of Fig. 2, the windings S2 P are arranged side byside, but in the case of the transformer 20 there is a small shunt 25which separates the two windings. This provides additional leakagereactance for the winding S2 if desired.

The transformers 2E! and. 29' are formed with the ends of the windinglegs 22 seated in appropriately mating joints such as shown at 2i and28. Leakage reactance may be increased and likelihood of saturationdecreased by providing an additional gap at 23'. The shunts 23 have gaps5B and the shunt 25 has gaps 3|.

In Fig. 1, the construction of the apparatus and the characters ofreference are identical to the construction and reference characters ofFig. 5, except that I have removed the condenser C' of Fig. 5 and havesubstituted instead another condenser C1. The electrical conductorbetween the junction I and the left hand terminal of the secondsecondary winding S2 has been opened and another condenser C12 has beeninserted therein.

Under normal conditions the apparatus of Fig. 1 will operate exactly thesame as the apparatus of Fig. 5. The condensers C1 and C2 are chosensuch that their combined capacitance is substan tially the same as thecapacitance of the condenser C of Fig. 5. Thus, if the example referredto for operation in connection with a pair of 40 watt T-12 fluorescentlamps uses a condenser C with a capacitance of 2.6 micro-farads and arating of 440 volts, then the condensers Cl and C2 for use with themodified apparatus will each have a capacitance of 5.2 micro-farads, butneed only have a voltage rating of 220 volts. The increased size of thecondensers is oifset cost- 7 wise by the fact that less expensiveinsulation may be used.

In the event that the fluorescent lamp L2 becomes faulty, such that itbegins to function as a rectifier, no direct current can pass throughthe winding S1 because it is blocked by the condenser C2. Therefore, thewinding S1 will not heat up, and certainly not burn-out. The lamp L2will therefore become extinguished, since no current can pass throughthe series connected winding S2 either. This indicates immediately thatthe lamp L2 is defective. During operation, the series capacitance ofthe condensers C1 and C2 is the same as a condenser C having half thecapaci" tance of either and placed .in the lead it. Dur ing ignition ofthe lamp L1- the condenser C1 serves the same purposeas the condenser Cnot withstanding its higher capacitance and lower voltage rating.

In Fig. 4, I have shown a modified form of the circuit with theinvention embodied therein. Thus, the same arrangement of windings isused as previously described except that the primary winding P isconnected such that its voltage sense as indicated by the arrow l'i' isopposed to the voltage sense of the winding Si as indicated by the arrowl8 and is additive to thevoltage sense of the winding S2 indicated bythe arrow l8. In this case the lamp L1.is connected across the windingS1 alone by the leads l3 and and the lamp L2 is connected across allthree windings by the leads l and I6. On open circuit, the voltageacross all windings is the resultant of the voltages of all threewindings, and sincethe two windings P and 62 are in opposition to thevoltage of the winding S1, said resultant is insufficient to ignite thelamp L2. The voltage induced in winding S1 is however suificient toignite lamp L1 and thereafter, due to the high leakage reactance of thewinding S1, a voltage is produced in S1 having component additive to thevoltages of the windings P and 8.2. At this time the lamp L2 ignites.

Again, the circuit as described and claimed in my previous patent has acondenser placed of Fig. 5, i. e., in the lead l4. If the lamp L2 lee--came defective and commenced to rectify, the direct current flowing inthe winding 51 would either heat it dangerously or burn it out. Itherefore utilize the same modification as described in connection withFig. l. I place one condenser C1 in the lead l4 and another condenser C2in the electrical connection between the juncture l l and the secondsecondary winding S2. The capacitance of each of the condensers C1 andC2 may be about twice that of a single condenser placed in series withthe lamp L1, and the voltage rating half of such single condenser (whichis not shown). The operation and benefits are the same as described inconnection with Fig. 1.

Note that the placement of the condenser C1 may be in the leads E3 or M,and that the placement of the condenser C2 may be at any place ofconvenience in that branch of the circuit which includes the winding S2,leads l5 and i5, and the lamp L2.

In another modified form shown in Fig. 6, the second condenser C2 isspaced between juncture ll and the right handend of the winding Si. Inthis case, the condenser C1 need not be changed in value from thecapacitance of con denser C1 while condenser C2 may be of lower ratingand relatively larger capacitance. There will be very little change instarting characteristics for lamp L1, but a slight decrease in totalavailable starting'voltagefor lamp L2.

asC-

The circuits illustrated herein and in connection with which I haveillustrated and described my invention are capable of wide variation andapplication. In all cases where a winding equivalent to the firstsecondary winding S1 is used having a large number of turns and finewire, the same is capable of being protected by the use of the inventionherein. For example, I have applied the invention of my previous PatentNo. 2,558,293 to ballasts having more than two gaseous discharge devicesassociated therewith, and the herein invention'is suitable for usetherewith and contemplates coverage thereof.

It is desired that the scope of the invention be commensurate with theclaims appended hereto as interpreted in their broadest sense in view ofthe prior art.

I claim:

1. In apparatus of the character described for igniting and thereafterregulating the operation of a gaseous discharge device from a source ofA. C. voltage substantially less than the igniting voltage of thedevice, which comprises a multiple winding transformer having a primarywinding, a pair of secondary windings arranged in voltage buckingrelationship one to the other with respect to a circuit containing bothsecondary windings, the primary, a first secondary, and

the second secondary windings being connected one after the other in theorder named an electrically conducting path connected across windingmeans of the transformer including at least the first secondary andexcluding the second secondary, a series capacitor in said path and agaseous discharge device connected across windings of .the saidtransformer including at least both secondaries, the said firstsecondary winding having a high leakage reactance and being a startingwinding such .that substantially all discharge device current lay-passesthe same through said electrically conducting path during operation,means for preventing flow of direc-t current through said firstsecondary winding in the event that the said gaseous discharge devicecommences rectifying, comprising a sec- 0nd capacitor in series with thesaid second secondary winding.

2. Apparatus as described in claim. 1 in which the value of capacitanceof each of said capacitors is approximately equal to two times thecapacitance required for power factor correction of the series operatingcircuit including the second secondary winding.

3. In apparatus of the character described for igniting and thereafterregulating the operation of a pair of gaseous discharge devices from asource of A. C. voltage substantially less than the ignition voltage ofthe devices, which comprises a transformer having a primary winding, afirst secondary winding, and a second secondary winding, the windingsallbeing mounted on a unitary iron core with the first secondary windingvery loosely coupled relative to the primary so as to provide a highleakage reactance therein, and the windings all being connected end toend in the order named but with the voltage sense of the secondariesreversed one relative to the other, an electrical path having a firstgaseous discharge device and a series capacitor therein and extendingacross windings of the transformer including at least the firstsecondary and excluding the second secondary, and a second gaseousdischarge device connected across windings of the transformer includingat least the secondaries in the resulting loop, means for preventing theflow of direct current through the first secondary in the event ofrectifying operation of the said second gaseous discharge device whichcomprises a second capacitor in series with the said second secondarywinding.

4. In a device of the character described adapted to seriatim ignite andseries operate a pair of gaseous discharge devices from a low voltage A.C. source and which comprises a three-winding transformer made up of aprimary winding, a high leakage reactance first secondary winding, and asecond secondary winding, the windings being connected end to end in theorder named, and in which electrical leads are provided connecting onedevice in a conducting loop which includes the said first winding butnot the secondary winding, and which loop has a series capacitortherein, and leads are provided connecting the second device in a secondconducting loop which includes the second secondary series-connectedtherein, means for blocking flow of D. C. current resulting fromabnormal operation of the second gaseous discharge device through thesaid first secondary winding without in any way afiecting the normaloperation of the apparatus which comprises a series capacitor in saidsecond conducting loop.

5. In a device of the character described adapted to seriatim ignite andseries operate a pair of gaseous discharge devices from a low voltage A.C. source and which comprises a three-winding transformer having a highleakage resistance first secondary winding electrically connectedbetween a primary winding and a second secondary winding, and in whichthe said first secondary winding is formed of a great number of windingsof fine wire compared with the other windings, and is in reverse voltagerelationship to the second secondary winding, and in which one device isconnected in a loop having a series capacitor, said loop including theprimary and first secondary windings, and in which the second device isconnected in a second loop including both of the said secondaries, theturn ratios of the windings being such that when the primary winding isenergized first the first device will ignite and then a voltage will beproduced in the first secondary winding additive to the voltage of thesecond secondary winding whereby to cause ignition of the second device,and thereafter due to the high leakage reactance of the said firstsecondary winding substantially all the current will flow in seriescircuit including the devices, the capacitor, and the second secondarywinding, the said first secondary winding being by-passed, the hereininvention which comprises means for preventing flow of direct currentthrough the said first secondary winding due to abnormal operation ofthe second device comprising a second condenser connected in series withthe said second secondary winding at a point in said second loop whereall of the current passing through the said second secondary windingwill be required to pass through said second capacitor.

6. The structure of claim 5 in which each capacitor has a capacitanceapproximately twice that required for power factor correction of saidseries circuit.

7. Apparatus of the character described adapted to ignite and operate apair of gaseous discharge devices from an A. C. source of relatively lowvoltage which includes an auto-transformer having a primary, two gaseousdischarge devices, a loosely coupled first secondary having one sideconnected to one side of said primary and in additive voltagerelationship thereto, and a loosely coupled second secondary having oneside connected to the second side of said first secondary and in voltagebucking relationship to the primary, means including a capacitivereactor connecting one of said devices across the primary and firstsecondary, the second of said devices being connected across the firstand second secondaries together, the source being connected across theprimary, and a second capacitive reactor inserted in the connectionbetween first and second secondaries.

8. Apparatus of the character described adapted to ignite and operate apair of gaseous discharge devic s from an A. C. source of relatively lowvoltage which includes a transformer having a. primary winding, twogaseous discharge devices, a loosely coupled first secondary windinghaving one side connected to one side of said primary winding and inreverse voltage relationship thereto, and a loosely coupled secondsecondary winding having one side connected to the second side of thesaid firsu secondary winding and being in bucking voltage relationshipthereto but in additive voltage relationship with the primary winding,one of said devices being connected in series with a capacitive reactorand together therewith being connected across the first secondarywinding only, the second device being connected across all threewindings together, the source being connected across the primarywinding, and a second capacitive reactor connected in series with thesecond device.

9. Apparatus of the character described which comprises a pair ofgaseous discharge devices, a source of A. C. voltage of a valuesubstantially less than the igniting voltage of either of the devices, athree winding auto-transformer having a unitary iron core and mountingthree windings comprising a primary winding, a first secondary windingand a second secondary winding, the primary winding being disposed inthe center of the core and having a magnetic shunt between itself andthe first secondary winding, the second secondary winding being closercoupled to the primary winding than the first secondary winding, theprimary winding being connected across the source, one terminal of theprimary winding being connected to one terminal of the first secondarywinding, one of said devices being in series with a condenser andtogether with the condenser connected from the second terminal of theprimary winding to the second terminal of the first secondary winding,the second device being in a, series circuit with a second condenser andthe second secondary winding and the said series circuit being connectedfrom the second terminal of the first secondary winding to the firstterminal of the first secondary winding, the instantaneous voltagesenses of the secondaries being bucking one relative to the other.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,346,621 Sola Apr. 11, 1944 2,436,399 Nathanson Feb. 24, 19482,436,400 Nathanson Feb. 24, 1948

